Recently there are many studies on mechanisms and therapeutic agents for various diseases caused by immune disorders and immune depression due to side effects of carcinostatic agents. It is known that thymulin, nonapeptide produced in thymus, shows a recovering effect for depressed immunity by conforming a complex with zinc. Therefore, thymulin has a possibility to be applied for treatment of immunodeficiency and autoimmune diseases. But there are many unclear points about the actions of thymulin, and few studies on synthetic compounds showing thymulin-like effects have been made.
Thymulin is a very small amount substance produced in thymus and easily decomposed by enzyme existing in living body because thymulin is a natural product. Therefore, there are many problems to apply thymulin to clinical use. Considering the action mechanism of thymulin, namely thymulin shows effects by conforming a complex with zinc, we synthesized various amino acid derivatives having sulfur atoms and examined the effects thereof comparing with thymulin.